Shells and growth?

Hello From Boston

So here’s my story. Yesterday, I went looking for two moon shells
that rotated in opposite directions But, every shell on the beach, I
look at went in the same direction. So, I stopped and scratch my head
full of sand. why can I find a shell to match the one I had in my

Does anybody know where I can find species of shell that has opposing
growth rotations, not just clock wise?


I would think the top and bottom of a shell specimen would give you
what you’re looking for. J.Z.Dule

travis - you have to go to opposite coasts of the country to get
opposite opening shells in most variaties - they’re called atlantic
or pacific opening - scallops are a good example: the little hinge
’wing’ is either on the left or the right - if you DO start seeing an
opposite opening one while you’re walking with your head down -
better start walking back quickly, you’ve circumnavigated the coast -

Interesting you should ask that – in 20,000 Leagues Under The Sea,
the main protagonist undergoes an epiphany when he finds a shell that
goes the wrong way (counterclockwise) – it foreshadows the doom of
the enigmatic Captain Nemo, etc. etc. as it is “an abomination of
Nature” or whatever (my quotes, not Jules’).

Anyway, as far as I know, shells only grow clockwise – but I’m not a
malacologist. I do hope someone gets a chuckle out of remembering the
ol’ Jules Verne, though.

  • Kieran

Hello from Auckland

Does anybody know where I can find species of shell that has opposing
growth rotations, not just clock wise? 

You won’t find ‘handedness’ in a univalve shell- no left hand and
right hand versions. Wouldn’t it be nice! Scientists have studied
handedness in plants and animals and it’s really quite a fascinating
subject … meanwhile, you need to
look for a bivalve mollusc. Here the scallop is a bivalve, as it is
everywhere, I guess.

You need a shell book.
Then you need to look for the bivalves.



B r i a n A d a m J e w e l l e r y E y e w e a r
@Brian_Adam1 ph/fx +64 9 817 6816 NEW ZEALAND photos from Australia!! Jewellery Events on now

Travis, nearly all univalve mollusks (“snails”) are right handed
(called “dextral”). The whorls are clockwise, the aperture is on the
right. There are very few exceptions. One is the Perverse Whelk
(Busycon perversum), uncommon and native to S.E. and eastern Mexico.
Another is the Lightning Whelk (Busycon contrarium), more common and
native to the eastern US. (Left handed shells are called
"sinistral".) If you were able to find a shell which was sinistral,
you would still be unable to find a matching shell of the same species
that coiled in the opposite direction.

Many bivalve mollusks (clams, scallops, etc.) also have very a faint
shallow spiral to their textural patterns, that originates from the
hinge area. The opposing halves will have patterns which “spiral”
(“curve” would be a more accurate word) in opposite directions. Afraid
this is the closest you’re going to get to “matching and opposite”.

What Ive says about going to the opposite coast to get “opposite
opening shells” may be true for certain species of scallops (although
there are Pacific scallops which have wings on both the right and the
left). However, it isn’t true that if you go to the other coast the
whorls of a univalve will switch to being left handed. Nope. Taint so.

I am curious about the shells of the Southern hemisphere, though. Do
they coil in the opposite direction like water going down a drain?

Rene Roberts
Beachcomber DIW (Dyed In the Wool)

Travis, I vaguely remember reading somewhere that the two hemispheres
produce shells with opposite growth direction. Don’t remember which
is which. The only way I know of to obtain opposites on the same
beach would be to split the shell through the midline producing two
mirror image halves.

Pam Chott


What you want will be tricky to find because of molluscan biology.
The majority of univalve [i.e. snail type] molluscs grow with a
rotation to the left, counterclockwise. It is extremely rare to find
one that grows clockwise, although it does happen. There is one
species where it is more common, but the odds are still very much
against you. And there are a few species that buck the curve and
always grow clockwise, but only rarely counterclockwise.

If you want mirror symmetry in shells for a design [as for earrings],
try using bivalves – the clam, mussel, and scallop type. Or you can
saw a univalve in half, the way many ammonite fossils are sold.

Pairs of univalve shells of identical species that grow in opposite
directions are much sought after by collectors because they are so
difficult to find. Such a pair would probably have more value to a
collector than it would as an article of jewelry.

Good luck,

Dr. Dule…You are exactly correct when the two sides of the
shell are synnetrical as is the case of the nautilus shell. I suspect
that the shell in question has the spiral on top and the open side
Sol K.


Apologies to all – Rene is quite right that the majority of univalve
shells are right-handed (dextral). I had one of those moments where
you say one thing while seeing something else in your mind’s eye.
[Something about the left brain/right brain stuff. My husband knows
that if I wave to him to turn a certain direction in the car, he
should turn the direction of the moving hand, not the direction of the
words I use. “Go left here,” I say, pointing with my right hand to the
right. So he goes right, which is what I wanted.]

Anyway, Travis, there is a terrific shell book that explains all this
in clear terms. It is a short, fascinating read and it changed not
only the way that I look at shells, but also the way I think about
shell-forming, as in synclastic and anticlastic raising, and in
spicula forming. The book is called A Natural History of Shells, and
it is by Geerat J. Vermeij, a Dutch scientist who is probably the
world’s most articulate expert on this subject. It is published by
Princeton University Press [ISBN 0-691-08596-X, 1993], has great
illustrations. I have used it for design ideas, and for generating
assignments for my students.

Good luck,

No need to apologize, Anne; I suspect that you were just mentally
viewing the shell from the bottom, in which case it would appear to be
growing counter-clockwise! Thanks for the shell book info. I’m going
to check it out also. (Can’t have too many shell books. Like tools.)

Just a additional tiny point to be nit picky heRe: if you cut a
univalve mollusk in half as some have suggested, you still won’t get
"matching opposite" halves. It’s because they don’t have bilateral
symmetry. The aperture will always be only on one side and there’s
really no way to bisect it. (The ammonites and nautilus shells are
different because they they are completely different kinds of
mollusks, and they are symmetrical.) If the shell is large enough, you
can cut it into little “slabs”, however, and some of the slabs will be
close to matchable.

Rene Roberts